Various techniques for spinal stabilization or fusion are known in the art. Such techniques often utilize surgical implants which mechanically immobilize areas of the spine and may include eventual incorporation of grafting material. One technique for spinal fixation includes immobilization of the spine by the use of rods that run generally parallel to the spine. In practicing this technique, the posterior surface of the spine is exposed, and bone screws are first fastened to the pedicles of the appropriate vertebrae or to the sacrum, acting as anchor points for the rods. The bone screws are generally placed two per vertebrae, one at each pedicle on either side of the spinous process. Fasteners join the spine rods to the screws. Some techniques employ anterior fixation devices (i.e., devices position in the anterior side of the vertebrae with screws going into the bodies of the respective vertebrae), in alternative to or in combination with, the posterior devices described above.